Continuous process for the use of metal carbonyls for the production of nano-scale metal particles

ABSTRACT

A process for producing nano-scale metal particles includes feeding at least one metal carbonyl into a reactor vessel; exposing the metal carbonyl to a source of energy sufficient to decompose the metal carbonyl and produce nano-scale metal particles; and depositing or collecting the nano-scale metal particles.

TECHNICAL FIELD

The present invention relates to a continuous process for the productionof nano-scale metal particles using metal carbonyls. The resultingnano-scale metal particles are useful for catalysis and other purposes.By the practice of the present invention, nano-scale metal particles canbe produced from metal carbonyls and deposited or collected with greaterspeed, precision and flexibility than can be accomplished withconventional processing. Thus, the invention provides a practical andcost-effective means for preparing such nano-scale metal particles.

BACKGROUND OF THE INVENTION

Catalysts are becoming ubiquitous in modern chemical processing.Catalysts are used in the production of materials such as fuels,lubricants, refrigerants, polymers, drugs, etc., as well as playing arole in water and air pollution mediation processes. Indeed, catalystshave been ascribed as having a role in fully one third of the materialgross national product of the United States, as discussed by Alexis T.Bell in “The Impact of Nanoscience on Heterogeneous Catalysis” (Science,Vol. 299, pg. 1688, 14 Mar. 2003).

Generally speaking, catalysts can be described as small particlesdeposited on high surface area solids. Traditionally, catalyst particlescan range from the sub-micron up to tens of microns. One exampledescribed by Bell is the catalytic converter of automobiles, whichconsist of a honeycomb whose walls are coated with a thin coating ofporous aluminum oxide (alumina). In the production of the internalcomponents of catalytic converters, an aluminum oxide wash coat isimpregnated with nanoparticles of a platinum group metal catalystmaterial. In fact, most industrial catalysts used today include platinumgroup metals especially platinum and iridium or alkaline metals likecesium, at times in combination with other metals such as iron ornickel.

The size of these particles has been recognized as extremely significantin their catalytic function. Indeed it is also noted by Bell that theperformance of a catalyst can be greatly affected by the particle sizeof the catalyst particles, since properties such as surface structureand the electronic properties of the particles can change as the size ofthe catalyst particles changes.

In his study on nanotechnology of catalysis presented at the Frontiersin Nanotechnology Conference on May 13, 2003, Eric M. Stuve of theDepartment of Chemical Engineering of the University of Washington,described how the general belief is that the advantage of the use ofnano-sized particles in catalysis is due to the fact that the availablesurface area of small particles is greater than that of largerparticles, thus providing more metal atoms at the surface to optimizecatalysis using such nano-sized catalyst materials. However, Stuvepoints out that the advantages of the use of nano-sized catalystparticles may be more than simply due to the size effect. Rather, theuse of nanoparticles can exhibit modified electronic structure and adifferent shape with actual facets being present in the nanoparticles,which provide for interactions which can facilitate catalysis. Indeed,Cynthia Friend, in “Catalysis On Surfaces” (Scientific American, April1993, p. 74), posits catalyst shape, and, more specifically, theorientation of atoms on the surface of the catalyst particles, asimportant in catalysis. In addition, differing mass transportresistances may also improve catalyst function. Thus, the production ofnano-sized metal particles for use as catalysts on a more flexible andcommercially efficacious platform is being sought. Moreover, otherapplications for nano-scale particles are being sought, whether for theplatinum group metals traditionally used for catalysis or other metalparticles.

Conventionally, however, catalysts are prepared in two ways. One suchprocess involves catalyst materials being deposited on the surface ofcarrier particles such as carbon blacks or other like materials, withthe catalyst-loaded particles then themselves being loaded on thesurface at which catalysis is desired. One example of this is in thefuel cell arena, where carbon black or other like particles loaded withplatinum group metal catalysts are then themselves loaded at themembrane/electrode interface to catalyze the breakdown of molecularhydrogen into monatomic hydrogen, for its separation into its componentprotons and electrons, with the resulting electrons passed through acircuit as the current generated by the fuel cell; on the opposingsurface, molecular oxygen is separated into monatomic oxygen foreventual combination with the proton and electron to form water. Onemajor drawback to the preparation of catalyst materials through loadingon a carrier particle is in the amount of time the loading reactionstake, which can be measured in hours in some cases.

To wit, in U.S. Pat. No. 6,716,525, Yadav and Pfaffenbach describe thedispersing of nano-scale powders on coarser carrier powders in order toprovide catalyst materials. The carrier particles of Yadav andPfaffenbach include oxides, carbides, nitrides, borides, chalcogenides,metals and alloys. The nanoparticles dispersed on the carriers can beany of many different materials according to Yadav and Pfaffenbach,including precious metals such as platinum group metals, rare earthmetals, the so-called semi-metals, as well as non-metallic materials,and even clusters such as fullerenes, alloys and nanotubes.

Alternatively, the second common methods for preparing catalystmaterials involves directly loading catalyst metals such as platinumgroup metals on a support without the use of carrier particles which caninterfere with the catalytic reaction. For example, many automotivecatalytic converters, as discussed above, have catalyst particlesdirectly loaded on the aluminum oxide honeycomb which forms theconverter structure. The processes needed for direct deposition ofcatalytic metals on support structures, however, are generally operatedat extremes of temperature and/or pressures. For instance, one suchprocess is chemical sputtering at temperatures in excess of 1,500° C.and under conditions of high vacuum. Thus, these processes are difficultand expensive to operate.

In an attempt to provide nano-scale catalyst particles, Bert andBianchini, in International Patent Application Publication No. WO2004/036674, suggest a process using a templating resin to producenano-scale particles for fuel cell applications. Even if technicallyfeasible, however, the Bert and Bianchini methods require hightemperatures (on the order of 300° C. to 800° C.), and require severalhours. Accordingly, these processes are of limited value.

Taking a different approach, Sumit Bhaduri, in “Catalysis With PlatinumCarbonyl Clusters,” Current Science, Vol. 78, No. 11, 10 June 2000,asserts that platinum carbonyl clusters, by which is meant polynuclearmetal carbonyl complexes with three or more metal atoms, have potentialas redox catalysts, although the Bhaduri publication acknowledges thatthe behavior of such carbonyl clusters as redox catalysts is notunderstood in a comprehensive manner. Indeed, metal carbonyls have beenrecognized for use in catalysis in other applications.

Metal carbonyls have also been used as, for instance, anti-knockcompounds in unleaded gasolines. However, more significant uses of metalcarbonyls are in the production and/or deposition of the metals presentin the carbonyl, since metal carbonyls are generally viewed as easilydecomposed and volatile resulting in deposition of the metal and carbonmonoxide.

Generally speaking, carbonyls are transition metals combined with carbonmonoxide and have the general formula M_(x)(CO)_(y), where M is a metalin the zero oxidation state and where x and y are both integers. Whilemany consider metal carbonyls to be coordination compounds, the natureof the metal to carbon bond leads some to classify them asorganometallic compounds. In any event, the metal carbonyls have beenused to prepare high purity metals, although not for the production ofnano-scale metal particles. As noted, metal carbonyls have also beenfound useful for their catalytic properties such as for the synthesis oforganic chemicals in gasoline antiknock formulations.

Accordingly, what is needed is a continuous process for the productionof nano-scale metal particles for use as, e.g., catalyst materials. Thedesired process can be used for the preparation of nano-scale particlesloaded on a carrier particle but, significantly, can also be used forthe deposition of nano-scale particles directly on a surface without therequirement for extremes in temperature and/or pressures.

SUMMARY OF THE INVENTION

A process for the production of nano-scale metal particles using metalcarbonyl starting materials is presented. By nano-scale particles ismeant particles having an average diameter of no greater than about1,000 nanometers (nm), e.g., no greater than about one micron. Morepreferably, the particles produced by the inventive system have anaverage diameter no greater than about 250 nm, most preferably nogreater than about 20 nm.

The particles produced by the invention can be roughly spherical orisotropic, meaning they have an aspect ratio of about 1.4 or less,although particles having a higher aspect ratio can also be prepared andused as catalyst materials. Aspect ratio refers to the ratio of thelargest dimension of the particle to the smallest dimension of theparticle (thus, a perfect sphere has an aspect ratio of 1.0). Thediameter of a particle for the purposes of this invention is taken to bethe average of all of the diameters of the particle, even in those caseswhere the aspect ratio of the particle is greater than 1.4.

In the practice of the present invention, a metal carbonyl is fed into areactor vessel and sufficient energy to decompose the carbonyl applied,such that the carbonyl decomposes and nano-scale metal particles aredeposited on a support or in a collector. The carbonyl employed in theinvention depends on the nano-scale metal particles desired to beproduced. In other words, if the desired nano-scale particles comprisenickel and iron, the metal carbonyls employed can be nickel carbonyl,Ni(CO)₄,and iron carbonyl, Fe(CO)₅; likewise, if noble metal nano-scalemetal particles are sought, then noble metal carbonyls are used as thestarting materials. In addition, polynuclear metal carbonyls such asdiiron nonacarbonyl, Fe₂(CO)₉, triiron dodecocarbonyl, Fe₃(CO)₁₂,decacarbonyldimanganese, Mn₂(CO)₁₀; indeed, many of the noble metalcarbonyls can be provided as polynuclear carbonyls, such asdodecacarbonyltriruthenium, Ru₃(CO)₁₂, andtri-μ-carbonylnonacarbonyltetrairidium, Ir₄(CO)₁₂. Indeed, heteronuclearcarbonyls, like Ru₂O_(s)(CO)₁₂, Fe₂Ru(CO)₁₂ and Zn[Mn(CO)₅]₂ are knownand can be employed in the production of nano-scale metal particles inaccordance with the present invention. Indeed, the polynuclear metalcarbonyls can be particularly useful where the nano-scale metalparticles desired are alloys or combinations on more than one metallicspecie.

The metal carbonyls useful in producing nano-scale metal particles inaccordance with the present invention can be prepared by a variety ofmethods, many of which are described in “Kirk-Othmer Encyclopedia ofChemical Technology,” Vol. 5, pp. 131-135 (Wiley Interscience 1992). Forinstance, metallic nickel and iron can readily react with carbonmonoxide to form nickel and iron carbonyls, and it has been reportedthat cobalt, molybdenum and tungsten can also react carbon monoxide,albeit under conditions of higher temperature and pressure. Othermethods for forming metal carbonyls include the synthesis of thecarbonyls from salts and oxides in the presence of a suitable reducingagent (indeed, at times, the carbon monoxide itself can act as thereducing agent), and the synthesis of metal carbonyls in ammonia. Inaddition, the condensation of lower molecular weight metal carbonyls canalso be used for the preparation of higher molecular weight species, andcarbonylation by carbon monoxide exchange can also be employed.

The synthesis of polynuclear and heteronuclear metal carbonyls,including those discussed above, is usually effected by metathesis oraddition. Generally, these materials can be synthesized by acondensation process involving either a reaction induced bycoordinatively unsaturated species or a reaction between coordinativelyunsaturated species in different oxidation states. Although highpressures are normally considered necessary for the production ofpolynuclear and heteronuclear carbonyls (indeed, for any metal carbonylsother than those of transition metals), the synthesis of polynuclearcarbonyls, including manganese, ruthenium and iridium carbonyls, underatmospheric pressure conditions is also believed feasible.

It must be borne in mind in working with the metal carbonyls, that carein handling must be used at all times, since exposuire to metalcarbonyls can be a serious health threat. Indeed, nickel carbonyl isconsidered to be one of the more poisonous inorganic industrialcompounds. While other metal carbonyls are not as toxic as nickelcarbonyl, care still needs to be exercised in handling them.

The processing of the metal carbonyls to form nano-scale metal particlesutilizes an apparatus comprising a reactor vessel, at least one feederfor feeding or supplying the metal carbonyl into the reactor vessel, asupport or collector which is operatively connected to the reactorvessel for deposition or collection of nano-scale metal particlesproduced on decomposition of the carbonyl, and a source of energycapable of decomposing the carbonyl. The source of energy should act onthe metal carbonyl(s) employed such that the carbonyl(s) decompose toprovide nano-scale metal particles which are deposited on the support orcollected by the collector.

The reactor vessel can be formed of any material which can withstand theconditions under which the decomposition of the carbonyl occurs.Generally, where the reactor vessel is a closed system, that is, whereit is not an open ended vessel permitting reactants to flow into and outof the vessel, the vessel can be under subatmospheric pressure, by whichis meant pressures as low as about 250 millimeters (mm). Indeed, the useof subatmospheric pressures, as low as about 1 mm of pressure, canaccelerate decomposition of the carbonyl and provide smaller nano-scaleparticles. However, one advantage of the inventive process is theability to produce nano-scale particles at generally atmosphericpressure, i.e., about 760 mm. Alternatively, there may be advantage incycling the pressure, such as from sub-atmospheric to generallyatmospheric or above, to encourage nano-deposits within the structure ofthe support. Of course, even in a so-called “closed system,” there needsto be a valve or like system for relieving pressure build-up caused, forinstance, by the generation of carbon monoxide (CO) from decompositionof the metal carbonyl or other by-products. Accordingly, the use of theexpression “closed system” is meant to distinguish the system from aflow-through type of system as discussed hereinbelow.

When the reactor vessel is a “flow-through” reactor vessel, that is, aconduit through which the reactants flow while reacting, the flow of thereactants can be facilitated by drawing a partial vacuum on the conduit,although no lower than about 250 mm is necessary in order to draw thereactants through the conduit towards the vacuum apparatus, or a flow ofan inert gas such as argon can be pumped through the conduit to thuscarry the reactants along the flow of the inert gas.

Indeed, the flow-through reactor vessel can be a fluidized bed reactor,where the reactants are borne through the reactor on a stream of afluid. This type of reactor vessel may be especially useful where thenano-scale metal particles produced are intended to be loaded on supportmaterials, like carbon blacks or the like, or where the metal particlesare to be loaded on an ion exchange or similar powdered resinousmaterial.

The at least one feeder supplying the carbonyl into the reactor vesselcan be any feeder sufficient for the purpose, such as an injector whichcarries the metal carbonyl along with a jet of a gas such as an inertgas like argon, to thereby carry the carbonyl along the jet of gasthrough the injector nozzle and into the reactor vessel. The gasemployed can be a reactant, like oxygen or ozone, rather than an inertgas. This type of feeder can be used whether the reactor vessel is aclosed system or a flow-through reactor.

Supports useful in the practice of the invention can be any material onwhich the nano-scale metal particles produced from decomposition of themetal carbonyl can be deposited. In a preferred embodiment, the supportis the material on which the catalyst metal is ultimately destined, suchas the aluminum oxide honeycomb of a catalytic converter in order todeposit nano-scale particles on catalytic converter components withoutthe need for extremes of temperature and pressure required by sputteringand like techniques. Alternatively, a collector suitable for collectionof the nano-scale metal particles for re-use, such as a cyclonic orcentrifugal collector, can be employed.

The support or collector can be disposed within the reactor vessel(indeed this is required in a closed system and is practical in aflow-through reactor). However, in a flow-through reactor vessel, theflow of reactants can be directed at a support positioned outside thevessel, at its terminus, especially where the flow through theflow-through reactor vessel is created by a flow of an inert gas.Alternatively, in a flow-through reactor, the flow of nano-scale metalparticles produced by decomposition of the carbonyl can be directed intoa centrifugal or cyclonic collector which collects the nano-scaleparticles in a suitable container for future use.

The energy employed to decompose the carbonyl can be any form of energycapable of accomplishing this function; indeed, the type or intensity ofenergy employed can depend on the type of carbonyl being decomposed. Forinstance, electromagnetic energy such as infrared, visible, orultraviolet light of the appropriate wavelengths can be employed.Additionally, microwave and/or radio wave energy, or other forms ofsonic energy can also be employed (example, a spark to initiate“explosive” decomposition assuming suitable moiety and pressure),provided the metal carbonyl is decomposed by the energy employed. Thus,microwave energy, at a frequency of about 2.4 gigahertz (GHz) orinduction energy, at a frequency which can range from as low as about180 hertz (Hz) up to as high as about 13 mega Hz, can be employed. Askilled artisan would readily be able to determine the form of energyuseful for decomposing the metal carbonyls which can be employed in theinventive process.

Because of the relatively low decomposition temperature of metalcarbonyls, generally less than about 150° C., and often less than about80° C., one preferred form of energy which can be employed to decomposethe carbonyl is heat energy supplied by, e.g., heat lamps, radiant heatsources, or the like. In such case, the temperatures needed are nogreater than about 250° C. to ensure effective decomposition of a highpercentage of the metal carbonyls in the reactor vessel. Indeed,generally, temperatures no greater than about 200° C. are needed todecompose the carbonyl to effectively produce nano-scale metal particlestherefrom.

Depending on the source of energy employed, the reactor vessel should bedesigned so as to not cause deposit of the nano-scale metal particles onthe vessel itself (as opposed to the support or collector) as a resultof the application of the source of energy. In other words, if thesource of energy employed is heat, and the reactor vessel itself becomesheated to a temperature at or somewhat higher than the decompositiontemperature of the carbonyl during the process of applying heat to thecarbonyl to effect decomposition, then the carbonyl will decompose atthe walls of the reactor vessel, thus coating the reactor vessel wallswith nano-scale metal particles or even bulk metal deposits rather thandepositing the particles on a support or collecting the nano-scale metalparticles with the collector (one exception to this general rule occursif the walls of the vessel are so hot that the metal carbonyl decomposeswithin the reactor vessel and not on the vessel walls, as discussed inmore detail below).

One way to avoid this is to direct the energy directly at the support orcollector. For instance, if heat is the energy applied for decompositionof the metal carbonyl, the support or collector can be equipped with asource of heat itself, such as a resistance heater in or at a surface ofthe support or collector such that the support or collector is at thetemperature needed for decomposition of the carbonyl and the reactorvessel itself is not. Thus, decomposition occurs at the support orcollector and formation of nano-scale particles occurs principally atthe support or collector. When the source of energy employed is otherthan heat, the source of energy can be chosen such that the energycouples with the support or collector, such as when microwave orinduction energy is employed. In this instance, the reactor vesselshould be formed of a material which is relatively transparent to thesource of energy, especially as compared to the support or collector.

Similarly, especially in situations when the support or collector isdisposed outside the reactor vessel when a flow-through reactor vesselis employed with a support or collector at its terminus (whether the asolid substrate collector for producing and depositing of nano-scalemetal particles thereon or a cyclonic or like collector for collectingthe nano-scale metal particles for deposit in a suitable container), thedecomposition of the decomposable carbonyl occurs as the metal carbonylis flowing through the flow-through reactor vessel and the reactorvessel should be transparent to the energy employed to decompose thecarbonyl. Alternatively, whether or not the support or collector isinside the reactor vessel, or outside it, the reactor vessel can bemaintained at a temperature below the temperature of decomposition ofthe carbonyl, where heat is the energy employed. One way in which thereactor vessel can be maintained below the decomposition temperatures ofthe metal carbonyl is through the use of a cooling medium like coolingcoils or a cooling jacket. A cooling medium can maintain the walls ofthe reactor vessel below the decomposition temperatures of the carbonyl,yet permit heat to pass within the reactor vessel to heat the metalcarbonyl and cause decomposition of the carbonyl and production ofnano-scale metal particles.

In an alternative embodiment which is especially applicable where boththe walls of the reactor vessel and the gases in the reactor vessel aregenerally equally susceptible to the heat energy applied (such as whenboth are relatively transparent), heating the walls of the reactorvessel, when the reactor vessel is a flow-through reactor vessel, to atemperature substantially higher than the decomposition temperature ofthe decomposable moiety can permit the reactor vessel walls tothemselves act as the source of heat. In other words, the heat radiatingfrom the reactor walls will heat the inner spaces of the reactor vesselto temperatures at least as high as the decomposition temperature of thedecomposable moiety. Thus, the moiety decomposes before impacting thevessel walls, forming nano-scale particles which are then carried alongwith the gas flow within the reactor vessel, especially where the gasvelocity is enhanced by a vacuum. This method of generatingdecomposition heat within the reactor vessel is also useful where thenano-scale particles formed from decomposition of the decomposablemoiety are being attached to carrier materials (like carbon black) alsobeing carried along with the flow within the reactor vessel. In order toheat the walls of the reactor vessel to a temperature sufficient togenerate decomposition temperatures for the decomposable moiety withinthe reactor vessel, the walls of the reactor vessel are preferablyheated to a temperature which is significantly higher than thetemperature desired for decomposition of the decomposable moiety(ies)being fed into the reactor vessel, which can be the decompositiontemperature of the decomposable moiety having the highest decompositiontemperature of those being fed into the reactor vessel, or a temperatureselected to achieve a desired decomposition rate for the moietiespresent. For instance, if the decomposable moiety having the highestdecomposition temperature of those being fed into the reactor vessel isnickel carbonyl, having a decomposition temperature of about 50° C.,then the walls of the reactor vessel should preferably be heated to atemperature such that the moiety would be heated to its decompositiontemperature several (at least three) millimeters from the walls of thereactor vessel. The specific temperature is selected based on internalpressure, composition and type of moiety, but generally is not greaterthan about 250° C. and is typically less than about 200° C. to ensurethat the internal spaces of the reactor vessel are heated to at least50° C.

In any event, the reactor vessel, as well as the feeders, can be formedof any material which meets the requirements of temperature and pressurediscussed above. Such materials include a metal, graphite, high densityplastics or the like. Most preferably the reactor vessel and relatedcomponents are formed of a transparent material, such as quartz or otherforms of glass, including high temperature glass commercially availableas Pyrex® materials.

Thus, in the process of the present invention, at least one metalcarbonyl is fed into a reactor vessel where it is exposed to a source ofenergy sufficient to decompose the carbonyl and produce nano-scale metalparticles. The metal carbonyl is fed into a flow-through reactor wherethe flow is created by drawing a vacuum or flowing an inert gas throughthe flow-through reactor. The energy applied is sufficient to decomposethe carbonyl in the reactor or as it as flowing through the reactor, andfree the metal from the carbonyl and thus create nano-scale metalparticles which are deposited on a support or collected in a collector.Where heat is the energy used to decompose the carbonyl, temperatures nogreater than about 250° C., more preferably no greater than about 200°C. are required to produce nano-scale metal particles, which at thesurface of the substrate for which they are ultimately intended withoutthe use of carrier particles and in a process requiring only seconds andnot under extreme conditions of temperature and pressure.

In one embodiment of the inventive process, a single feeder feeds asingle carbonyl into the reactor vessel for formation of nano-scalemetal particles. In another embodiment, however, a plurality of feederseach feeds metal carbonyls into the reactor vessel. In this way, allfeeders can feed the same carbonyl or different feeders can feeddifferent carbonyls, such as additional metal carbonyls, so as toprovide nano-scale particles containing different metals such asplatinum-nickel combinations or nickel-iron combinations as desired, inproportions determined by the amount of the carbonyl fed into thereactor vessel by each feeder. For instance, by feeding differentcarbonyls through different feeders, one can produce a nano-scaleparticle having a core of a first metal, with domains of a second orthird, etc. metal coated thereon. Indeed, altering the carbonyl fed intothe reactor vessel by each feeder can alter the nature and/orconstitution of the nano-scale particles produced. In other words, ifdifferent proportions of metals making up the nano-scale particles, ordifferent orientations of the metals making up the nano-scale particlesis desired, altering the metal carbonyl fed into the reactor vessel byeach feeder can produce such different proportions or differentorientations.

Indeed, in the case of the flow-through reactor vessel, each of thefeeders can be arrayed about the circumference of the conduit formingthe reactor vessel at approximately the same location, or the feederscan be arrayed along the length of the conduit so as to feed metalcarbonyls into the reactor vessel at different locations along the flowpath of the conduit to provide further control of the nano-scaleparticles produced.

While it is anticipated that the inventive process and apparatus mayalso produce particles that are larger than nano-scale in size alongwith the nano-scale particles desired, the larger particles can beseparated from the sought-after nano-scale particles through the use ofthe cyclonic separator or because of their differing deposition rates ona collector.

Therefore it is an object of the present invention to provide acontinuous process for the production of nano-scale metal particlesusing metal carbonyl starting materials.

It is another object of the present invention to provide a continuousprocess capable of producing nano-scale metal particles under conditionsof temperature and/or pressure less extreme than conventional processes.

It is still another object of the present invention to provide acontinuous process for preparing nano-scale metal particles which can beformed on the end use substrate.

It is yet another object of the present invention to provide acontinuous process for preparing nano-scale metal particles which can becollected for further use or treatment.

These objects and others which will be apparent to the skilled artisanupon reading the following description, can be achieved by feeding atleast one metal carbonyl into a reactor vessel comprising a conduit;exposing the metal carbonyl within the reactor vessel to a source ofenergy sufficient to decompose the metal carbonyl and produce nano-scalemetal particles; and depositing or collecting the nano-scale metalparticles. Preferably, the temperature within the reactor vessel is nogreater than about 250° C. The pressure within the reactor vessel ispreferably generally atmospheric, but pressures which vary between about1 mm to about 2000 mm can be employed.

The reactor vessel is advantageously formed of a material which isrelatively transparent to the energy supplied by the source of energy,as compared to either the support or collector or the metal carbonyl,such as where the source of energy is a source of radiant heat. In fact,the support or collector can have incorporated therein a resistanceheater, or the source of energy can be a heat lamp. Where the energy isheat, a cooling medium such as cooling coils or a cooling jacket can bedisposed about the reactor vessel to cool the vessel.

The support can be the end use substrate for the nano-scale metalparticles produced, such as a component of an automotive catalyticconverter or a fuel cell or electrolysis membrane or electrode. Thesupport or collector can be positioned within the reactor vessel.However, the support collector can be disposed either external to thereactor vessel or within the reactor vessel.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe invention, and are incorporated in and constitute a part of thisspecification. The drawings illustrate various embodiments of theinvention, and together with the description serve to explain theprinciples and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side plan view of an apparatus for the production ofnano-scale metal particles from metal carbonyl starting materialsutilizing a “closed system” reactor vessel in accordance with theprocess of the present invention.

FIG. 2 is a side plan view of an alternate embodiment of the apparatusof FIG. 1.

FIG. 3 is a side plan view of an apparatus for the production ofnano-scale metal particles from metal carbonyl starting materialsutilizing a “flow-through” reactor vessel in accordance with the processof the present invention.

FIG. 4 is an alternative embodiment of the apparatus of FIG. 3.

FIG. 5 is another alternative embodiment of the apparatus of FIG. 3,using a support external to the flow-through reactor vessel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, an apparatus for the production ofnano-scale metal particles is generally designated by the numeral 10 or100. In FIGS. 1 and 2 apparatus 10 is a closed system comprising closedreactor vessel 20 whereas in FIGS. 3-5 apparatus 100 is a flow-throughreaction apparatus comprising flow-through reactor vessel 120.

It will be noted that FIGS. 1-5 show apparatus 10, 100 in a certainorientation. However, it will be recognized that other orientations areequally applicable for apparatus 10. For instance, when under vacuum,reactor vessel 20 can be in any orientation for effectiveness. Likewise,in flow-through reactor vessel 120, the flow of inert carrier gas andmetal carbonyls or the flow of metal carbonyls as drawn by a vacuum (orcombinations thereof) in FIGS. 3-5 can be in any particular direction ororientation and still be effective. In addition, the terms “up” “down”“right” and “left” as used herein refer to the orientation of apparatus10, 100 shown in FIGS. 1-5.

Referring now to FIGS. 1 and 2, as discussed above apparatus 10comprises a closed-system reactor vessel 20 formed of any materialsuitable for the purpose and capable of withstanding the exigentconditions for the reaction to proceed inside including conditions oftemperature and/or pressure. Reactor vessel 20 includes an access port22 for providing an inert gas such as argon to fill the internal spacesof reactor vessel 20, the inert gas being provided by a conventionalpump or the like (not shown). Similarly, as illustrated in FIG. 2, port22 can be used to provide a vacuum in the internal spaces of reactorvessel 20 by using a vacuum pump or similar device (not shown). In orderfor the reaction to successfully proceed under vacuum in reactor vessel20, it is not necessary that an extreme vacuum condition be created.Rather negative pressures no less than about 1 mm, preferably no lessthan about 250 mm, are all that are required.

Reactor vessel 20 has disposed therein a support 30 which can beattached directly to reactor vessel 20 or can be positioned on legs 32 aand 32 b within reactor vessel 20. Reactor vessel 20 also comprises asealable opening shown at 24, in order to permit reactor vessel 20 to beopened after the reaction is completed to remove support 30 or removenano-scale metal particles deposited on support 30. Closure 24 can be athreaded closure or a pressure closure or other types of closingsystems, provided they are sufficiently air tight to maintain inert gasor the desired level of vacuum within reactor vessel 20.

Apparatus 10 further comprises at least one feeder 40, and preferably aplurality of feeders 40 a and 40 b, for feeding reactants, morespecifically the carbonyl starting materials, into reactor vessel 20. Asillustrated in FIGS. 1 and 2, two feeders 40 a and 40 b are provided,although it is anticipated that other feeders can be employed dependingon the nature of the carbonyl(s) introduced into vessel 20 and/or endproduct nano-scale metal particles desired. Feeders 40 a and 40 b can befed by suitable pumping apparatus for the carbonyl such as venturi pumpsor the like (not shown).

As illustrated in FIG. 1, apparatus 10 further comprises a source ofenergy capable of causing decomposition of the metal carbonyl. In theembodiment illustrated in FIG. 1, the source of energy comprises asource of heat, such as a heat lamp 50, although other radiant heatsources can also be employed. In addition, as discussed above, thesource of energy can be a source of electromagnetic energy, such asinfrared, visible or ultraviolet light, microwave energy, radio waves orother forms of sonic energy, as would be familiar to the skilledartisan, provided the energy employed is capable of causingdecomposition of the carbonyl.

In one embodiment, the source of energy can provide energy that ispreferentially couple-able to support 30 so as to facilitate deposit ofnano-scale metal particles produced by decomposition of the carbonyldirectly on support 30. However, where a source of energy such as heatis employed, which would also heat reactor vessel 20, it may bedesirable to cool reactor vessel 20 using, e.g., cooling tubes 52 (shownpartially broken away) such that reactor vessel 20 is maintained at atemperature below the decomposition temperature of the carbonyl. In thisway, the metal carbonyl does not decompose at the surfaces of reactorvessel 20 but rather on support 30.

In an alternative embodiment illustrated in FIG. 2, support 30 itselfcomprises the source of energy for decomposition of the carbonyl. Forinstance, a resistance heater powered by connection 34 can beincorporated into support 30 such that only support 30 is at thetemperature of decomposition of the metal carbonyl, such that thecarbonyl decomposes on support 30 and thus produces nano-scale metalparticles deposited on support 30. Likewise, other forms of energy fordecomposition of the carbonyl can be incorporated into support 30.

Support 30 can be formed of any material sufficient to have depositthereon of nano-scale metal particles produced by decomposition of thecarbonyl. In a preferred embodiment, support 30 comprises the end usesubstrate on which the nano-scale metal particles are intended to beemployed, such as the aluminum oxide or other components of anautomotive catalytic converter, or the electrode or membrane of a fuelcell or electrolysis cell. Indeed, where the source of energy is itselfembedded in or associated with support 30, selective deposition of thecatalytic nano-scale metal particles can be obtained to increase theefficiency of the catalytic reaction and reduce inefficiencies or wastedcatalytic metal placement. In other words, the source of energy can beembedded within support 30 in the desired pattern for deposition ofcatalyst metal, such that deposition of the catalyst nano-scale metalcan be placed where catalytic reaction is desired.

In another embodiment of the invention, as illustrated in FIGS. 3-5,apparatus 100 comprises a flow-through reactor vessel 120 which includesa port, denoted 122, for either providing an inert gas or drawing avacuum from reactor vessel 120 to thus create flow for the metalcarbonyls to be reacted to produce nano-scale metal particles. Inaddition, apparatus 100 includes feeders 140 a, 140 b, 140 c, which canbe disposed about the circumference of reactor vessel 102, as shown inFIG. 3, or, in the alternative, sequentially along the length of reactorvessel 120, as shown in FIG. 4.

Apparatus 100 also comprises support 130 on which nano-scale metalparticles are collected. Support 130 can be positioned on legs 132 a and132 b or, in the event a source of energy is incorporated into support130, as a resistance heater, the control and wiring for the source ofenergy in support 130 can be provided through line 134.

As illustrated in FIGS. 3 and 4, when support 130 is disposed withinflow-through reactor vessel 120, a port 124 is also provided for removalof support 130 or the nano-scale metal particles deposited thereon. Inaddition, port 124 should be structured such that it permits the inertgas fed through port 122 and flowing through reactor vessel 120 toegress reactor vessel 120 (as shown in FIG. 3). Port 124 can be sealedin the same manner as closure 24 discussed above with respect to closedsystem apparatus 10. In other words, port 124 can be sealed by athreaded closure or pressure closure or other types of closingstructures as would be familiar to the skilled artisan.

As illustrated in FIG. 5, however, support 130 can be disposed externalto reactor vessel 120 in flow-through reactor apparatus 100, and canalso be a structural support 130 as illustrated in FIG. 5. In thisembodiment, flow-through reactor vessel 120 comprises a port 124 throughwhich reduced nano-scale metal particles are impinged on support 130 tothus deposit the nano-scale metal particles on support 130. In this wayit is no longer necessary to gain access to reactor vessel 120 tocollect either support 130 or the nano-scale metal particles depositedthereon. In addition, during the impingement of the reduced nano-scalemetal particles on support 130, either port 126 or support 130 can bemoved in order to provide for an impingement of the produced nano-scalemetal particles on certain specific areas of support 130. This isespecially useful if support 130 comprises the end use substrate for thenano-scale metal particles such as the component of a catalyticconverter or electrode for fuel cells. Thus, the nano-scale metalparticles are only deposited where desired and efficiency and decreaseof wasted catalytic metal is facilitated.

As discussed above, reactor vessel 20, 120 can be formed of any suitablematerial for use in the reaction provided it can withstand thetemperature and/or pressure at which decomposition of the carbonylstarting materials occurs. For instance, the reactor vessel should beable to withstand temperatures up to about 250° C. where heat is theenergy used to decompose the carbonyl. Although many materials areanticipated as being suitable, including metals, plastics, ceramics andmaterials such as graphite, preferably reactor vessels 20, 120 areformed of a transparent material to provide for observation of thereaction as it is proceeding. Thus, reactor vessel 20, 120 is preferablyformed of quartz or a glass such as Pyrex® brand material available fromCorning, Inc. of Corning, N.Y.

In the practice of the invention, either a flow of an inert gas such asargon or a vacuum is drawn on reactor vessel 20, 120 and a stream ofmetal carbonyl(s) fed into reactor vessel 20, 120 via feeders 40 a, 40b, 140 a, 140 b, 140 c. For instance, if heat is the source of energy,the carbonyl(s) should be subject to decomposition and production ofnano-scale metal particles at temperatures no greater than 250° C., morepreferably no greater than 200° C. Other materials, such as oxygen, canalso be fed into reactor 20, 120 to partially oxidize the nano-scalemetal particles produced by decomposition of the carbonyl, to protectthe nano-scale particles from further degradation. Contrariwise, areducing material such as hydrogen can be fed into reactor 20, 120 toreduce the oxidation of the particles and facilitate the production ofvery pure metal nano particles.

The energy for decomposition of the carbonyl is then provided to thecarbonyl within reactor vessel 20, 120 by, for instance, heat lamp 50,150. If desired, reactor vessel 120 can also be cooled by cooling coils52, 152 to avoid deposit of nano-scale metal particles on the surface ofreactor vessel 20, 120 as opposed to support 30, 130. Nano-scale metalparticles produced by the decomposition of the metal carbonyls are thendeposited on support 30, 130 or, in a cyclonic or centrifugal or othertype collector (not shown), for storage and/or use.

Thus the present invention provides a facile and continuous method forproducing nano-scale metal particles which permits selective placementof the particles, direct deposit of the particles on the end usesubstrate, without the need for extremes of temperature and pressurerequired by prior art processes.

All cited patents, patent applications and publications referred toherein are incorporated by reference.

The invention thus being described, it will be apparent that it can bevaried in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the present invention and allsuch modifications as would be apparent to one skilled in the art areintended to be included within the scope of the following claims.

1. A process for producing nano-scale metal particles, comprising: a) feeding at least one metal carbonyl into a flow-through reactor vessel; b) exposing the metal carbonyl to a source of energy sufficient to decompose the metal carbonyl and produce nano-scale metal particles; and c) depositing or collecting the nano-scale metal particles.
 2. The process of claim 1, wherein the temperature within the reactor vessel is no greater than about 250° C.
 3. The process of claim 2, wherein a vacuum is maintained within the reactor vessel of no less than about 1 mm.
 4. The process of claim 2, wherein a pressure of no greater than about 2000 mm is maintained with the reactor vessel.
 5. The process of claim 1, wherein the reactor vessel is formed of a material which is relatively transparent to the energy supplied by the source of energy, as compared to either a support or a collector on which the nano-scale metal particles are deposited or collected or the metal carbonyl.
 6. The process of claim 2, where the source of energy comprises a source of heat.
 7. The process of claim 6, wherein the nano-scale metal particles are deposited on a support
 8. The process of claim 7, wherein the support has incorporated therein a resistance heater.
 9. The process of claim 8, wherein the source of energy comprises a heat lamp.
 10. The process of claim 6, which further comprises cooling the reactor vessel.
 11. The process of claim 1, wherein the support is the end use substrate for the nano-scale metal particles produced.
 12. The process of claim 11, wherein the support comprises a component of an automotive catalytic converter.
 13. The process of claim 1, wherein the support is positioned within the reactor vessel.
 14. The process of claim 1, wherein the support or collector is disposed external to the reactor vessel.
 15. The process of claim 14, wherein the collector is a cyclonic collector.
 16. The process of claim 1, wherein oxygen is fed into the reactor vessel to partially oxidize the nano-scale metal particles produced by decomposition of the decomposable moiety.
 17. The process of claim 1, wherein a reducing material is fed into the reactor vessel to reduce the potential for oxidation of the decomposable moiety. 